1. Field of the Invention
The present invention relates to a flat vibration motor built into a mobile phone etc., more particularly relates to a structure of a stator plate for the same.
2. Description of the Related Art
In the past, as a flat vibration motor, for example a brushless motor has been provided with a stainless steel disk shaped base plate on which one end of a shaft is press fitted into a burring part, a stainless steel cover case having a cylindrical shape with a bottom with an open part covered by the base plate and to which the other end of the shaft is fitted in a shaft mounting hole, a rotor frame having an axial direction field type rotor magnet and eccentric weight supported to be able to rotate via a slide bearing through which the shaft runs, and a flexible printed circuit board superposed on the base plate and mounting a plurality of no-core coils, current control IC's, and other electronic devices. The base plate has a plurality of detent torque generating holes around the burring part for avoiding cessation of rotation at the dead points where the rotor magnet cannot be re-driven when energizing the no-core coils is stopped so that the cessation of rotation occurs at the points other than the dead points.
Here, the base plate, for convenience in feeding power to the required interconnect of the flexible printed circuit board, has an ear-shaped power feed terminal mount sticking out from the arc-shaped outer periphery outward in the radial direction. This is electrically connected to a power feed pattern on the device side board mounting this flat vibration motor through this flexible printed circuit board on this power feed terminal mount. Further, the base plate is provided at a plurality of locations with detent torque generating holes. Due to this, there is the problem of entry of solder into these holes, so the plate has mounting legs sticking out from the arc-shaped outer periphery outward in the radial direction and can be fastened to the device side board mounting the flat vibration motor by reflow solder.
As related art, there is Japanese Patent Publication (A) No. 2005-27484 (FIG. 2).
In reflow processing at a high temperature (250° C. for example) when the above flat vibration motor is mounted on the device side board, the shapes of the bobbin-less no-core coils are deformed so that the magnetic flux of the no-core coils will be in disorder and the gaps between no-core coils and the rotor magnet will have various values, resulting in that the yield rate of the flat vibration motor will be greatly reduced.